MM is from New Brunswick CA--as I saw a post of his a week or 2 back. that is part of the CA maritimes east coast region.
As to the original topic, it all depends. here is some food for thought...
I see dogs on the TV shows hunting below freezing temps--but often they have a perm heated blind. That makes a huge difference when they are wet and can get warm and out of the wind.
Or if they can run around on land to keep warm helps too.
But if they is wet and it's cold out and they is stuck in a boat so no running around and ne heat, a person is courting arthritis in their dog IMO.
I guess a person needs to determine what their dog is for. Some use them strictly as retreiving machines. Some as a family pet. Some for both. So one has to weigh the possible risks. For me my dog is my buddy and also is to retreive downed birds. So I try keep them out of the water when the water/air temp is too cold for me that I need to wear gloves. Especially dead easily retrived birds via a boat, I will use the boat when cold out. But on occasion I'll send the dog on a cripples retreive. So I guess I limit their exposure. Those (like guides) whose dog is in the cold water all the time often retire their dog by age 8--they have gotten arthritis so bad
And I think the thick wet suits are great, I have the extra flotation too on the back to help them out. It can really make adifference if the dog tires or gets caught up in thick weeds or a decoy line--as that bouyancy helps. I had friends dog drown in warm water (2nd week) a number of years ago when it got caught up in the decoy lines. It left an impression on me--not to send a dog in harms way. Thus I limit my dogs exposure to potential harms. Kind of like being a good Dad/guardian in a way similar with kids. My dog is my buddy, simple as that, and I look out for my buds in life regardless if 2 or 4 legged ones.